A method, already in clinical use, of determining the total volume of the heart in patients in the supine position was evaluated. The reproducibility in the measurement of individual diameters and distances was good. A minor difference was noted between the results of 2 different examiners. A discrepancy in the total heart volume of 30 ml or more between 2 determinations was statistically significant, which may be a guide in the assessment of volume determinations in clinical practice.